In general, to assure that an internal combustion engine has an increased combustion efficiency and an increased output, it is required that it has an improved combustion matching. To have such an improved combustion matching, items required particularly for a fuel injection system are such that a period of time for injecting a required amount of fuel is shortened as far as possible and moreover uniformity of distribution of sprayed fuel in a combustion chamber is improved further.
Hitherto, a nozzle in the fuel injection device used for a conventional internal combustion engine, particularly for a conventional high speed diesel engine is usually so designed that a plurality of injection holes formed at the fore end part of the injection nozzle are arranged in a single row on the periphery of a circle of which center coincides with a center axis of the injection nozzle which has 4 to 6 injection holes formed thereon so that combustion matching and uniformity of distribution of injected fuel are improved. However, required performances fail to be attained at present.
To assure that a period of fuel injection time is shortened further to improve combustion matching with such a high speed diesel engine, it has been considered that respective injection holes formed at the fore end part of the injection nozzle should preferably have an enlarged diameter, in other words, have an increased total area. However, when the injection holes have an increased total area merely by enlarging their diameter, it has been found that a streaming force generated by fuel injection becomes excessively intense, then this causes fuel injection to be achieved in a deviated state on a periphery area of the combustion chamber and this leads to a high magnitude of fluctuation in distribution of injected fuel in the combustion chamber, resulting in a combustion efficiency being reduced adversely. Accordingly an excessively enlarged diameter of the respective injection holes can not contribute to improvement in combustion efficiency with the internal combustion engine and increase in output therefrom.
In addition, it has been considered that when the number of injection holes is increased without any increase in diameter thereof, their total area is likewise increased and this enables a period of fuel injection time to be shortened. However, when the number of injection holes is practically increased, it follows that a distance between adjacent injection holes is reduced and this causes overlapping to occur between successive spray injections even with a reduced intensity of swirl in the combustion chamber, resulting in a high magnitude of fluctuation in distribution of sprayed fuel appearing in the combustion chamber. Accordingly, the conventional internal combustion engine can not improve a combustion efficiency thereof and increase an output therefrom irrespective of how much the number of injection holes is immoderately increased.
On the other hand, with the foregoing circumstances in mind, the inventors have proposed a fuel injection nozzle under Japanese Utility Model Application NO. 195511/1982 of which purport consists in that an area assumed by injection holes is increased, depth of a cavity is determined more than that of a conventional non-swirl type combustion chamber and a period of fuel injection time is shortened as far as possible to improve uniformity of distribution of sprayed fuel in the combustion chamber.
The injection nozzle proposed under Japanese Utility Model Application NO. 195511/1982 is so designed that a plurality of injection holes are arranged in two upper and lower rows concentrically relative to the center axis of the injection nozzle, center axes of the radially extending injection holes in the upper row coincide with those in the lower row at a single position on the center axis of the injection nozzle and the injection holes in the upper row are arranged in a zigzag fashion relative to those in the lower row. When injection holes are arranged in that way, it follows that the number of injection holes is increased to increase their total area and a period of fuel injection time is shortened. Additionally, since the injection holes are arranged in a zigzag fashion, a danger that overlapping occurs between fuel injections effected through adjacent injection holes is removed as far as possible, resulting in uniformity of distribution of injected fuel being improved as far as possible. The injection nozzle proposed under Japanese Utility Model Application NO. 195511/1982 is shown in FIG. 13 which is a fragmental sectional view illustrating the fore end part of the injection nozzle.
According to the prior invention proposed under Japanese Utility Model Application NO. 195511/1982 as shown in FIG. 13, the injection nozzle is so constructed that a plurality of injection holes arranged in upper and lower rows in a zigzag fashion are formed concentrically relative to the center axis L of the injection nozzle in such a manner that their radially extending center axes P and P'. are converged on a single position 0 on the center axis L. Thus, starting points Q and Q'. of the respective injection holes arranged in the upper and lower rows have a reduced distance therebetween, causing a crack to occur between adjacent injection holes after the injection nozzle is used for a long period of time. Consequently, the injection nozzle has a degraded durability. In other words, the conventional internal combustion engine including the aforementioned injection nozzle has a degraded durability.
The present invention has been made with the foregoing background in mind and its object resides in providing an internal combustion engine which assures that a period of time required for injecting a required amount of fuel is determined as short as possible, uniformity of distribution of sprayed fuel in a combustion chamber is improved further and moreover durability of an injection nozzle is improved further.
Other object of the present invention is to provide an internal combustion engine which assures that a period of fuel injection time is shortened, uniformity of distribution of sprayed fuel in the combustion chamber is improved, depth of a cavity is determined more than that of a conventional non-swirl type combustion chamber and moreover the injection nozzle has an excellent durability.
Another object of the present invention is to provide an internal combustion engine which assures that the cavity serving as a combustion chamber has a shallow-bottomed sectional contour corresponding to an increased output from the engine, a period of fuel injection time is shortened even with such a combustion chamber having a shallow-bottomed sectional contour, uniformity of distribution of sprayed fuel in the combustion chamber is improved and moreover the injection nozzle has an excellent durability.